Dynamic Response of the Entrance Structure of an Elliptical Mountain Tunnel under the Action of SH Waves

Generally, the surrounding rock at the entrance of a mountain tunnel is loose, and the entrance has more slopes due to topography, which causes the tunnel entrance section to be easily destroyed under an earthquake. Based on the established slope model with a single free surface, this paper adopted the elastic wave theory to derive the analytical solution of the strain at the entrance of the mountain tunnel when the SH wave is incident perpendicularly to the bottom of the tunnel; besides, the factors affecting strain were also analyzed. The tangential strain curve at each point of the entrance section takes the centre of the elliptical tunnel as the centre of symmetry, forming symmetry between the left and right sides and mirror symmetry between the top and bottom sides. Then, large-scale shaking table model experiments were conducted to model the actual working conditions, and the correctness of the analytical solution was verified. The research can provide a theoretical reference for the seismic design of the entrance section of the high-speed railway tunnel and greatly improve the understanding of its seismic response.

An Improved GPR Method Based on BP and RPCA for Tunnel Lining Defects Detection and Its Application in Qiyue Mountain Tunnel, China

Tunnel lining defects are one of the most common problems that tunnels experience during operation, and they can pose severe safety risks. The most popular nondestructive testing method for detecting tunnel lining defects is ground penetrating radar (GPR), one of the basic geophysical applications. However, detection responses might differ significantly from the real shape of tunnel lining defects, making it challenging to identify and interpret. When data quality is poor, interpretation and identification become more challenging, resulting in a high cost of tunnel repairs. The improved back projection (BP) imaging and robust principal component analysis (RPCA) are used in this work to offer a GPR data processing method. Even in the event of poor data quality, our method could recover GPR responses, allowing the shapes and locations of tunnel lining flaws to be clearly depicted. With BP imaging, this approach recovers the tunnel defects’ responses to better forms and positions, and with RPCA, it further isolates the target imaging from clutters. Several synthetic data demonstrate that the approach presented in this work may successfully repair and extract the positions and forms of lining defects, making them easier to identify and comprehend. Furthermore, our technique was used to GPR data gathered from the Qiyue Mountain Tunnel in China, yielding more accurate findings than the traditional method, which was validated by the actual scenario to illustrate the efficiency of our method on real data.

Karst Geology in Southwest Hubei and Mitigation of Geohazards During Mountain Tunnel Through a Large Karst Cave

The outcrop area of carbonate rocks accounts for 61.6% of the total area in Southwest Hubei. The action of tectonic application, erosion of surface and underground water system, topography, and carbonate geology leads to the formation of large karst caves, and their features are as following: considerably large, long and narrow, winding and in different forms. Limited by route directions, large karst caves would be encountered during tunneling through mountains, therefore causing hazards such as instability of the karst cave, water or stone ingress, damage to the tunnel, and long-term instability. A case study of mountain tunnel through a large karst cave is presented. The large karst cave is formed due to the erosion of limestone by two underground river systems. The length, width and volume of the cavity of the large karst cave are about 139 m, 91 m and 4.3×105 m3. The large karst cave is overall stable without strong external factors. Engineering proposals and treatment of the large karst cave are introduced. The small pipe grouting method is used to treat the foundation. Two kinds of lining structure schemes are adopted, double lining open-cut tunnel structure, and traditional tunnel structure after backfill. The water outside the lining of the open-cut tunnel is introduced into the tunnel ditch and discharged through the tunnel drainage system. Monitoring and measurement during tunneling construction and operation process are introduced.